I don’t find the comment particularly strange nor do I your reaction in the rhetorical sense.
It’s generally accepted wisdom in society but particularly in traditional society even more so as an essential duty!
I’ve often heard stories of how one or all of a couple being seen to change for the better with the arrival of their first child, expressed as being “the making of them,” but with recent western society seeing a dramatic increase in adults without children, children with only one parent and many not in any form of long standing relationship let along married that perception is not as typically expressed or understood IMHO and is viewed with a lot of hostility. It hasn’t gone unremarked as to the childless nature of a lot of the current European heads of state.
I have noted Peterson often cites that there are typically three main events in peoples lives. Events which they do not forget that are formative seminal moments in their life with the birth of their first child being one of those three.
Another is Religious/Mystical experience and I’ve forgotten the other but I think it’s getting married but I’ll need to double check that one.
I think you’ll get a better feel for where he is coming if you listen to podcast No.2, Tragedy Vs Evil. I just so happened to listen to it today and he makes a nice observation point about how children introduces you to vulnerability and perfection in a very real and beautiful way and thus gives a deeper insight into what is essential a tweet.
If you’ve read Robert Anton Wilson (but original developed by Leary and similar if not a repackaging of the Chakras) becoming a parent is the 4th Circuit in Wilson’s analogy, though from the wiki you wouldn’t readily pick that up. If I remember correctly in Prometheus Rising Wilson has framed it in much simpler terms.
The next one after that become closer to transcendent as you go…